This invention relates generally to electrical connector assemblies and, more particularly, to bidirectional electromagnetic interference filter connector assemblies having high input/output attenuation and vice versa, over the frequency range of approximately 10 Mhz to 10 Ghz, and having very low external RF leakage, as well.
Electrical connectors having integral filter assemblies for attenuation of electrical interference are finding an increasing demand in the communication, data handling and aerospace industries. To meet this demand a wide variety of filter connector assemblies have been developed which utilized tubular ceramic capacitors, ferrite inductance ferrules and conductive elastomers of rubber or plastic. There features are used singly or in combination as a means of attenuating the transmission of undesired electromagnetic interference (EMI) through conductors terminated to the connectors by providing a low impedance path to ground for EMI. These filter assemblies also reduce EM radiation from a closed connector and lessen the susceptibility of a closed connector to pickup of externally generated EMI.
U.S. Pat. No. 3,579,155 describes a specially designed pin contact for use in a filtered EMI connector. This pin contact includes a row of closely coupled ferrite beads and a co-axial tubular ceramic capacitor with split inside metallic surfaces connected to opposite ends of the pin body by means of conductive elastic grommets. The single outer conductor of the capacitor has a shoulder which contacts a metal plate element for grounding purposes. The pin filter section of this prior art connector is installed between a front pin contact element and a rear element designed to retain a connecting wire with a crimp fitting. The metal shell which retains an apertured insulating plug body is in two pieces. In practice, it was observed that RF leakage occurred at the interface of the two sections or pieces. The reason for the conductive elastic supports for the ceramic capacitor of the above cited prior art patent is to protect it from stresses caused by slight pin misalignment and pin movement during connection and disconnection of the plug assembly.
U.S. Pat. No. 3,535,676 and U.S. Pat. No. 3,539,973 each describes an identical rectangular multi-pin chassis or bulkhead connector designed to accommodate filtered connector pin sockets or pin contacts. While these two patents differ in certain mechanical and design details, they both feature use of a deformable elastic, electrically conducting gasket placed between two sections of the dielectric apertured pin retaining body. The function of this elastic rubber or polymer conductive gasket is to ground the external conductor of the coaxial capacitors on the filtered connector pins. The holes in the conductive gasket are designed to make an interference fit with the filter pins. The resistivity of the gasket is designed to decrease when the connector is bolted together. Conductive laminates of foil or metal mesh are also mentioned as a means of reducing the series resistance in the ground lead of the filter pin capacitors and as a means of increasing pin to pin isolation. However, these residual gasket resistances are a source of parasitic coupling between pins which is very undesirable.
U.S. Pat. No. 3,721,869 describes a filter contact connector and a method of assembly using a resilient gasket. The filter element in this cited patent consists of a coaxial capacitor the external conductor of which is grounded by being pushed through a hole in an electrically conductive elastic insert which connects the capacitor body to the metallic outer shell of the connector. The conductive elastic insert is clamped between two halves of a dielectric pin socket retaining body which allows some clearance around each pin socket to facilitate alignment with a mating pin. The desired resilience is provided by the conductive elastic insert which grips the inserted pins. This disclosed prior art device does not utilize a decoupling element and the resistance of the conductive gasket can cause undesired parasitic coupling between pins.
U.S. Pat. No. 3,870,978 describes a connector using electrically conductive resilient material compressed between abutting electrical contacts for use where thermal expansion or contraction may cause a connection problem. This overcomes looseness or misalignment problems. Also disclosed is the placement of a ceramic capacitor between two compressed conductive resilient contact blocks in series with abutting contact pins within a connector to perform a D.C. isolation function in an RF line. The thermal resistance of the conductive resilient contact blocks will potentially cause heat dissipation problems under high current conditions.
U.S. Pat. No. 3,879,102 describes a coaxial cable connector which features an internal sleeve that supports a comparatively thin-walled rigid outer conductor. An internally threaded metal compression fitting clamps the outer conductor to the cable connector, which is in turn bolted to a bulkhead or chassis. The above mentioned compression fitting cooperates on its outer end with a rubber "O" ring which functions to make the fitting water and gas tight. The disclosure indicates that while the metal to metal contact at the inner end of the compression fitting usually provides adequate RF shielding, additional reduction of RF leakage may be obtained by using an electrically conductive "O" ring.
While filter connectors such as those disclosed in these prior art patents have met with considerable success, they nevertheless suffer from the disadvantages mentioned and are not suitable for certain applications where both EMI suppression and control of RF leakage are important. Accordingly, a need exists for an EMI filter connector assembly which is capable of providing a high degree of EMI attenuation, be free of RF leakage and be able to provide physical stress isolation between its contacts and the RF filter assembly. In addition, a need exists for such a connector which is also compatible with existing chassis and bulkhead connectors and may be retrofitted without expensive rewiring.